Disk-ring reactors used for the continuous production of polyesters have been known for some time. These are typically cylindrical, horizontal, heated vessels with inlet and outlet connections for the precondensate and polycondensate on opposite ends of the disk-ring reactor. The disk-ring reactor comprises a plurality of elements rotating about a horizontal axis, which elements mix the precondensate and produce a large surface for outgassing the polycondensate when the viscous liquefied material adhering to these elements runs down. Devices of this type are described in the German patent applications 1 745 541 (U.S. Pat. Nos. 3,499,873 and 3,617,225), 1 720 692 (U.S. Pat. No. 3,591,344), 2 100 615 (U.S. Pat. No. 3,684,458) and 2 114 080 (U.S. Pat. No. 3,761,059) as well as in European patents and patent applications 0 320 586 (U.S. Pat. No. 5,055,273), 0 719 582 (U.S. Pat. No. 5,779,986), 0 711 597 (U.S. Pat. No. 5,599,507) and 1 386 659.
The disadvantage with known disk-ring reactors is that polycondensate residue deposits on the inside wall of the reactor, resulting not only in encrustation and fouling of the reactor, but additionally producing a discolored product with undesirable inclusions if the product adheres to the inside reactor wall for an extended period and is exposed to high reaction temperatures, which result in thermal damage to and cross-linking of the polycondensate. Non-filterable, gel-like contamination interferes with the polymer-processing operation and in the end reduces the product quality.